The present invention relates generally to a method and apparatus for providing a forward error correction scheme for data transmission and specifically to an improved method for selecting error correction parameters.
The increasing volume of information communicated electronically has taxed the capacity of the communications infrastructure. One form of high-speed communication is Digital Subscriber Line (DSL) technology. DSL uses an infrastructure that already exists; namely, copper twisted pair lines typically used for telephone communication. However, only a small portion of the available bandwidth of the twisted pair line (0 to 4 kHz) is used for Plain Old Telephone Service (POTS). DSL takes advantage of the available frequency spectrum from 4 kHz to approximately 1.1 MHz for transmitting data over relatively short reaches.
Asymmetric DSL (ADSL) is the most widely implemented form of DSL technology. ADSL is asymmetric in that its downstream (to a subscriber) capacity is larger than its upstream (from the subscriber) capacity. Typically, a Discrete Multi-Tone (DMT) scheme is used. The spectrum from 4 kHz to 1.1 MHz is divided into 256 sub-channels, or tones, each having a bandwidth of 4.3125 kHz.
It is well known that the performance of an ADSL modem is generally limited by cross-talk. In order to improve system performance and capacity, an error-correcting code such as the Reed-Solomon (RS) code is used. Using error-correcting codes, a higher data rate or longer loop reach can be achieved for the same level of transmitted signal power. However, this can be optimized only by selecting appropriate error-correcting code parameters, such as code-word length (n) and redundant, or parity, length (r).
If large values are selected for the code-word length n and redundant length r, large coding gain can be achieved from error-correcting codes. However, a large value for r will have a large overhead loss. This leads to a trade-off in the choice of the value for r. Further, the selection of error-correcting code parameters depends on the transmission environment such as signal-to-noise ratio (SNR) distribution over multiple DMT tones. Thus, in practice the selection of the best possible error-correcting code parameters is very difficult.
Furthermore, this difficulty is not confined to DSL, but also applies to other communications technologies, such as cable modems, CD and DVD players, digital audio and broadcast, HDTV/Digital TV, data storage, wireless communications, wireless enabled personal digital assistants, digital satellite communication and broadcast, and Redundant Array of Independent Disk (RAID) controllers with fault tolerance.
It is an object of the present invention to obviate or mitigate the above-mentioned difficulties.